Figure 4. Experimental and numerical observation of Bloch oscillations in a system with a broken PT symmetry.

In all cases, the initial distribution is a Gaussian wavepacket occupying the upper band. Due to the partially complex band structure, the wavepacket is periodically amplified during Bloch oscillations. Note, that each time, the wavepacket passes through an exceptional point, a new branch of Bloch oscillations appears (secondary emissions). However, for resonant Bloch gradients ( in the experiment and in our simulation), a pseudo-Hermitian propagation is restored, where the total energy stays constant over many time steps. Here, the gain/loss coefficient is .